Porous bodies are solids containing many pores. The structure in which these pores are connected to each other is called interconnected cell structure. Porous bodies having the interconnected cell structure often have a property of absorbing liquid.
For example, polyurethane foams having the interconnected cell structure have been used widely as cleaning sponges for tableware, because of their favorable water-absorbing efficiency. In addition, polyurethane foams and phenol foams having the interconnected cell structure have been used as flower-arrangement holders. Interconnected cell porous bodies are used in this application because of their water-absorbing efficiency and such a product has a function to keep flowers fresh for an extended period of time. Alternatively, in the field of agriculture, interconnected-cell porous bodies obtained by bonding rock wools are being used as a medium for use for example in nutriculture. An interconnected-cell porous body used in this application has functions to hold firmly the root of plants to be cultivated and supply nutrient-containing water to the plants by absorbing it by itself.
As described above, interconnected-cell porous bodies are very useful. In addition, among the interconnected-cell porous bodies for use as flower-arrangement holders and media for example for plant nutriculture, those that are made of a biodegradable resin are easily decomposed in the environment and thus have an advantage that they can be disposed easily after use and thus, they are highly useful.
Patent Document 1 discloses, as such a biodegradable porous body, a porous polylactic acid material of a polymer containing lactic acid as a principal component and having interconnected pores of an average pore size of 1 to 30 μm. The porous body is prepared by dissolving a polymer containing lactic acid as a principal component and a copolymer of a water-soluble polyalkylene ether and lactic acid in a solvent, drying the solution to solid matter, and removing the copolymer by elution with another liquid. However, this production method is very complicated in procedure and has a problem that it easily leads to increase in cost. Although a film-shaped product can be prepared easily the production method also has problems that the interconnected structure can change easily during drying and it is difficult to obtain products with relatively larger thickness.
Alternatively, Patent Document 2 discloses an interconnected-cell body containing as a principal component a biodegradable plastic that is manufactured by blending, extruding, and expanding a mixture of a biodegradable resin, an expanding agent, an inorganic filler and others, and a flower-arrangement holder produced from the same. However, it is difficult to obtain a favorable interconnected cell structure only by molding a biodegradable plastic together with an expanding agent or the like. In addition, the extrusion expanding method has limitation in the shape of the molding obtained and does not always permit molding into a desired shape.
Yet alternatively, Patent Document 3 discloses use of a foam of an aliphatic polyester such as a polylactic acid resin as a flower-arrangement holder. However, the aliphatic polyester resin foam does not have a pore structure suitable for water absorption, although it is an interconnected cell foam, and thus absorbs water slowly and shows insufficient water-absorbing efficiency.
Patent Document 4 discloses a production method of preparing a foam by pressurizing expandable particles having a polymer coat in a mold, thus performing heating without use of steam, and describes that pulverized particles obtained from the foam by recycling were used as the expandable particles. However, Patent Document 4 uses preliminary expanded particles of an expandable polyolefin or styrene polymer as expandable particles and there is no description on biodegradable polymers in the Patent Document 4. Patent Document 4 also does not contain any description on pulverized particles obtained from the foam. Patent Document 4 further does not contain any description on foams having an interconnected cell structure.